March Moon Madness Arrives Early
Some of the most interesting bodies in the solar system are the objects not big enough to be called planets. Moons, asteroids and comets continue to yield their secrets and surprises. Here’s a quick rundown on recent findings.
Why do some asteroids look so fresh? It’s because they get a facelift, Space.com reported last month. As some asteroids wander close to earth, the tides can produce tremors and landslides. “This process could explain why many space rocks orbiting nearby appear pristine, as if they were covered in a new and clean surface, researchers said.” Normally, space weathering would redden the surfaces. Like humans, though, it would seem asteroids can only get a facelift a finite number of times. Clark Chapman at Nature News and Views indicated that this is only the latest suggestion to explain youthful surfaces on some near-earth asteroids (NEAs). “Our perceptions of NEAs are rapidly changing,” he said. “Perhaps soon, robotic or piloted docking missions to some of these NEA rubble piles will reveal the beautiful complexity of their evolving behaviour.”
Pluto belongs in this entry because it is no longer a planet, but a plutoid, or a minor planet, or a dwarf planet, or the IAU’s term du jour. It made the news recently for its seasonal changes. BBC News shows Hubble pictures of a mottled surface that has changed in just a few years as the angle of sunlight migrates. The article says that some astronomers have expressed “shock” at the observations. “It’s a little bit of a surprise to see these changes happening so big and so fast,”said Marc Buie, of the Southwest Research Institute. “This is unprecedented.”
The Cassini team, invigorated by the approval of its 7-year solstice mission (see Feb 3 press release from JPL), continues to explore the Saturn system with zest. The little moon Mimas, barely visible in an image released Feb 15, was a prime target for a Feb 13 flyby. The unprocessed images are now posted at the Imaging Team site. They show good views of its 140-km Herschel crater with its Everest-height central peak. Prometheus, one of the F-ring shepherd moons, gave Cassini its best-ever portrait last month.
The active moon Enceladus continues to be a newsmaker. Space.com repeated last month’s suggestion that the eruptive periods are episodic over billions of years (see 01/11/2010). Latest findings of negative ions in its geyser plumes (see JPL press release) strengthen the case for liquid water under its surface. Some scientists cannot resist the knee-jerk reaction of associating water with life. Science Daily made that angle its centerpiece; Space.com was only slightly more reserved. The water-means-life equation was presented ad nauseum in a new planet TV series from National Geographic, The Traveler’s Guide to the Planets, which aired beginning Feb 14. The visually-rich series includes new dazzling animations of the spacecraft and the best of the Cassini images, despite the obsession with evidence-free astrobiology.
Speaking of astrobiology, the BBC News declared that the Murchison meteorite that landed in Australia in 1969 contains an “organic molecular feast.” A new analysis by a German team counted 14,000 organic molecules so far; they estimate millions may exist in the rock’s innards. They think the rock predates the sun itself and picked up organics from the molecular clouds that became the sun. Somehow it titillates the astrobiological sense: “Where did we come from and what happened before? We all have that question inside us,” the lead researcher commented.
The biggest moons of the solar system made news recently. Some scientists think they have figured out the surface differences between Jupiter’s Ganymede and Callisto, reported Science Daily. The theory brings in the “Late Heavy Bombardment” hypothesis (LHB) and sees Ganymede getting the brunt of the energy by being closer to Jupiter’s gravity well. The extra energy led to Ganymede melting and getting a differentiated interior while Callisto just got pummeled on the surface. It’s not clear if the theory explains Io and Europa also, which are smaller and have very few craters due to internal activity. Richard Kerr at Science News of the Week for Jan. 29 quoted a Caltech astronomer calling this “an interesting idea” that’s “promising.” The Late Heavy Bombardment seems to be being employed as both an assumption and an explanation: Kerr said, “to the extent that it proves to be an attractive explanation of the dichotomy, it also lends support to the reality of the LHB.”
Titan, Saturn’s titanic moon, continues to get radar-scanned five years after the historic landing of the Huygens probe (see JPL feature story). The landing was dramatically animated in the National Geographic series mentioned earlier. Science Daily echoed a JPL press release showing strange grooved hills in the latest swath. PhysOrg and Space.com reported on work to reproduce the strange organic chemistry that produces flows, cryovolcanos and rivers on Titan’s surface. It’s hard to find stories about Titan without the L-word close at hand: “This study could also tell us about the chemistry that led to the origin of life on early Earth.” Three major papers on Titan’s atmosphere and surface appeared in this month’s Icarus; they will be reported here if time permits. Titanophiles will be glad to know a major hardback science book, Titan from Cassini-Huygens, has been released and is available from Amazon.com. It’s a companion of another book summarizing all of Cassini’s scientific results about Saturn, the rings, and the icy satellites (especially Enceladus), also available at Amazon.com, Saturn from Cassini-Huygens. Written by the Cassini scientists themselves, these two books contain the most current and authoritative information to date on the Saturn system.
Observations and hypotheses these days are so intertwined it becomes hard to separate them. Consider the suggestion that the Late Heavy Bombardment explains the Ganymede-Callisto dichotomy. One has to assume the LHB and the long ages. And consider the idea that tidal landslides explain the youthful surfaces of asteroids. How many times in 4 billion years can this occur before there is no more youthful skin underneath the rubble to expose? There is essentially no way to test these ideas without assuming the long ages of the consensus secular view of the solar system. Science will never establish the long ages this way. That’s the problem with assumptions. They are assumed, not demonstrated. Because the long ages are never allowed to become vulnerable to falsification, they become part of a self-perpetuating belief system that sometimes requires improbable contortions to maintain. The talk about life every time water is mentioned is fact-free speculation. It’s logic-free, too, because it would be just as corny to go off on tangents about life every time protons are found, because they also are building blocks of life. In the TV series, Chris McKay waxed eloquent about all the ingredients for life that exist at Enceladus: a heat source, organics, and water. We challenge him to put water, ammonia, ethane and carbon dioxide in a very cold sterile refrigerator, stir it occasionally, and wait for a very long time. At least he could give us some experimental evidence to back up his rhetoric. As long as one can filter out the speculative fluff in scientific stories, the rich discoveries about such varied and interesting worlds should be a delight to all who maintain a spirit of exploration.